Overlay Transport Virtualization (OTV) is an IP-based functionality that provides Layer 2 extension capabilities over any transport infrastructure, whether it be Layer 2 based, Layer 3 based, IP switched, label switched, etc. OTV provides an overlay that enables Layer 2 connectivity between separate Layer 2 network domains (e.g., separate virtual local area networks, or VLANs) while keeping these domains independent and preserving the fault-isolation, resiliency, and load-balancing benefits of an IP-based interconnection. A virtual local area network (VLAN) is a group of computers and/or other networked devices that communicate as if they were connected via a single network switch, regardless of their physical location. OTV uses a concept known as MAC routing, which means a control plane protocol is used to exchange MAC reachability information between network devices providing LAN extension functionality. An edge device performs the OTV functions of receiving Layer 2 traffic for all VLANs that need to be extended to remote locations and dynamically encapsulates the Ethernet frames into IP packets that are then sent across a transport infrastructure. The IS-IS standard routing protocol may be used to implement a control plane for OTV and provide the capability of carrying MAC address information in type-length-value (TLV) segments of data packets.
When multiple edge devices are connected between a set of VLANs and the overlay, an authoritative edge device (AED) election mechanism identifies a designated forwarder for the set of VLANs. In conventional systems, the AED election is triggered independently and is uncoordinated among the multiple edge devices in the site, so a short timeout period of blackholing traffic is required to ensure two or more edge devices are not simultaneously AED and hence forwarding traffic for the same VLAN. This introduces a convergence delay when there are failures at an edge device that is the AED for some VLANs. Furthermore, multiple simultaneous misconfigurations, such as with both site-VLAN and site-id, can lead to a failure to prevent loops. Additionally, arbitrary merging and/or partitions of individual VLANs cannot be optimally handled.